You can read the decision here. The decision applies to closely-held corporations (i.e. corporations for whom the majority of shares are held by five or fewer people) whom the Supreme Court feels can demonstrate a sincere religious conviction about contraception.
Closely held corporations employ around 29 million Americans, so they do not constitute only a few corporations, though it is perhaps true that only a few can demonstrate sincere religious beliefs. Furthermore, closely held corporations with fewer than 50 employees are not subject to the Affordable Care Act's mandate, and some may not provide any health insurance at all.
It is not clear to what degree this ruling would apply to other religious objections, as Ruth Bader Ginsburg pointed out in her dissent.
Would the exemption…extend to employers with religiously grounded objections to blood transfusions (Jehovah's Witnesses); antidepressants (Scientologists); medications derived from pigs, including anesthesia, intravenous fluids, and pills coated with gelatin (certain Muslims, Jews, and Hindus); and vaccinations[?]…Not much help there for the lower courts bound by today's decision.
Though Alito, writing for the majority, said that this decision does not require that all employee coverage mandates fail when they conflict with religious beliefs, without more precedent, we do not yet know what other coverage mandates could fail given a conflict.